Method for Producing a Coil and Electronic Device

ABSTRACT

The invention relates to a method for producing a coil integrated in a substrate or applied to a substrate, wherein the coil has first winding portions, which each have first ends and second ends, and wherein the coil has second winding portions and third winding portions, wherein each two of the first ends are electrically interconnected by the second winding portions and two corresponding second ends of the first winding portions are electrically interconnected by the third winding portions, such that coil windings of the coil are formed hereby, wherein at least the first winding portions are applied by means of a 3D printing method, wherein this is aerosol jet or inkjet printing, for example.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional application of and claims priority toU.S. patent application Ser. No. 14/069,413 filed on Nov. 1, 2013 andentitled “Method for Producing a Coil and Electronic Device,” which is anational stage application of and claims priority to German PatentApplication No. 10 2012 220022.3 filed on Nov. 2, 2012, both of whichare incorporated herein by reference in their entireties.

DESCRIPTION

The invention relates to a method for producing a coil integrated in asubstrate or applied to a substrate, in particular a method forproducing an electronic printed circuit board, and also an electronicdevice comprising such an electronic printed circuit board.

Planar coils in which the coil windings are applied to the surface of asubstrate are known per se from the prior art. Only a relatively lowinductance can be achieved cost-efficiently with such planar coils,wherein the planar coils additionally take up a relatively large amountof space on the substrate surface.

Embedded Faltflex coils are known from www.elektroniknet.de, 26 Apr.2012, “Embedding von aktiven und passive Bauteilen in die Leiterplatte”(“Embedding of active and passive components into the printed circuitboard”). Here, flexible film structures are folded such that coils canbe produced in any size with a practically arbitrary number of layers.This is particularly advantageous for sensor applications.

A coil structure for a printed circuit board arrangement is known fromDE 43 06 416 A1. A winding of the coil is formed by metallized bores andconductive track portions. A ferrite core can be introduced laterally ina slit in the printed circuit board. Alternatively, the inner layers ofthe printed circuit board can be used directly as a support forimprinted core structures. A disadvantage with this coil structure isthat on the one hand it is not suitable for miniaturization, and on theother hand large inductances cannot be achieved therewith.

An inductive sensor having a coil for generating a magnetic field isknown from DE 103 54 694 A1. The coil is formed by two layers, betweenwhich a strip of an amorphous metal is located as a coil core. The coilwindings are formed by conductive track portions arranged on the layersand by through-contactings, which run past on the coil core.

An inductive sensor which has a coil generating a magnetic field, thecore of said coil being provided in an aperture in a circuit carrier, isknown from DE 103 55 003 A1.

By contrast, the object of the present invention is to create animproved method for producing a coil integrated in a substrate orapplied to a substrate, in particular for producing a printed circuitboard, and also an electronic device comprising such a coil.

The objects forming the basis of the invention are each achieved by thefeatures in the respective independent patent claims. Embodiments of theinvention are specified in the dependent patent claims.

In accordance with embodiments of the invention, at least the firstwinding portions are applied by means of a 3D printing method, inparticular also the second winding portions and/or the third windingportions.

Here, a “3D printing method” is understood to mean any printing methodwhich enables three-dimensional electrical line structures to be appliedby means of printing, such as aerosol jet or inkjet printing methods. Inthe 3D printing method, electrically conductive inks, in particular anelectrically conductive polymer, silver conductive past or the like, isused in order to apply the line structures by means of printing.

Embodiments of the invention are particularly advantageous since the useof a 3D printing method makes it possible to introduce miniaturizedcoils into a substrate or to apply such coils to a substrate, moreoverat relatively low production costs and high throughput. In particular,the production of miniaturized coil arrays of high resolution andsensitivity is thus enabled, in particular for the production ofsensors, such as inductive proximity sensors, or actuators.

In accordance with embodiments of the invention, the following approachfor production of a coil is adopted, for example:

-   -   1. A substrate is first provided. The substrate may be a printed        circuit board material, in particular fiber-reinforced plastic,        in particular a glass fiber mat saturated with epoxy resin, for        example what is known as an FR-4 material.    -   2. A cavity is produced in the substrate and for example is open        toward the front face of the substrate. The cavity can be        produced in the substrate by material-removing processing of the        substrate, for example by removing the material with the aid of        a laser or by a machining process, preferably by milling and        also by hot foil stamping. The cavity has a base area, which for        example runs parallel to the surface of the substrate, and also        lateral flanks, which connect the base area to the surface of        the substrate.    -   3. Once the cavity has been produced, the first and second        winding portions of the coil are introduced into the cavity. The        first winding portions run along the flanks of the cavity and        extend from the base area to the surface of the substrate. The        second winding portions run along the base area, where they each        contact two ends of the first winding portions. The following        approach for example can be adopted in order to introduce the        first and second winding portions:    -   a) The two winding portions are first formed on the base area,        for example more specifically by a conventional structuring        technique, in particular the application of a copper layer and        subsequent etching, or by a two-dimensional printing method,        such as screen printing. The first winding portions are then        applied to the flanks of the cavity by means of the 3D printing        method. Alternatively, the first winding portions may also be        applied, and then the second winding portions.    -   b) The first and second winding portions are applied to the base        area and the flanks of the cavity in one process step with the        aid of the 3D printing method.    -   4. The cavity is then filled with a core material, for example a        paste, which contains ferromagnetic particles. Here, a paste is        understood to mean a mixture of a particle and a liquid, for        example a solvent, for example a suspension. Due to the        introduced paste, a core material is formed in the cavity and        serves to produce a coil core. Alternatively, the core material        may also be introduced in the form of a solid into the cavity,        for example by being pressed in.    -   5. The third winding portions are applied to the surface of the        resultant coil core, more specifically for example by a        structuring technique, in particular etching, or by means of a        printing method, in particular a 2D printing method.

By contrast, in accordance with embodiments of the invention, thefollowing approach for example is adopted in order to apply a coil to asubstrate:

-   -   1. A substrate is first provided. The substrate may be a printed        circuit board material, in particular fiber-reinforced plastic,        in particular a glass fiber mat saturated with epoxy resin, for        example what is known as an FR-4 material.    -   2. The second winding portions are applied to the surface of the        substrate, for example by means of a structuring technique or a        two-dimensional printing method.    -   3. In the region of the second winding portions, core material        is then applied to the surface of the substrate, with the result        that the core material covers the second winding portions. The        core material can be applied similarly to the above-mentioned        step 4 by applying a paste, for example using a dispenser, or by        applying a solid.    -   4. The first and third winding portions of the coil are then        applied, wherein the first winding portions extend along the        lateral flanks of the coil core and the third winding portions        extend over the surface of the coil core. To this end, one of        the following embodiments specified hereinafter can be adopted        for example:    -   a) The first and third winding portions are applied in one        process step by means of a 3D printing method.    -   b) Only the first winding portions are applied by means of a 3D        printing method, whereas the third winding portions are applied        for example by means of a structuring method or two-dimensional        printing method.

Different coil geometries can be produced in this way, such as acylindrical coil, of which the coil axis runs parallel to the surface ofthe substrate, or an annular or toroidal coil, which is orientedparallel to the surface of the substrate.

In accordance with an embodiment of the invention, the coil core in thecavity is annular, toroidal, or disk-shaped, wherein the coil core mayhave a round or angular shape. Due to the selection of other geometriesof the cavity and therefore of the coil core, the magnetic field to begenerated by the coil can be optimized for the respective application.

In accordance with an embodiment of the invention, the cavity has a basearea parallel to the surface of the substrate. Lateral flanks run outfrom the base area and form the opening of the cavity. The lateralflanks preferably form a right angle or an acute angle with the surfaceof the substrate, for example an angle between 30 and 60°, preferably45°.

Such an angle has the surprising advantage that air pockets are avoidedwhen introducing the paste into the cavity, since the air can escapealong the lateral flanks during the introduction process. This isparticularly advantageous when the paste is pressed into the cavity, forexample by means of screen printing, intaglio printing, pad printing, orwith the aid of a dispenser.

It has surprisingly proven to be particularly advantageous when thepaste is introduced by means of screen printing and the lateral flanksof the cavity enclose an angle of approximately 45° with the surface.

In accordance with an embodiment of the invention, the particles consistof a soft magnetic amorphous and/or nanocrystalline alloy.

Here, particles which have a nanocrystalline structure are particularlyadvantageous, since this leads to a very high permeability with a smallcoercive force. Further advantages of such nanocrystalline materials areoutstanding magnetic values, cost-effective alloy compositions, verygood temperature stability, and very favorable frequency properties. Thenanocrystalline particles can be composed from a soft magnetic metalalloy, for example based on Fe, Si and/or B with additions of Nb and/orCu.

In accordance with an embodiment of the invention, a plurality of theintegrated coils are produced in the substrate in this way. These coilscan be connected for example to a sensor array, for example in order toproduce a highly sensitive inductive position sensor.

In accordance with a further embodiment, the second winding portions canbe imprinted. The second winding portions can be imprinted for exampleby means of conductive inks: further circuit components, which may beformed by means of electrically conductive polymer, may likewise beimprinted on the substrate in order to connect this to the one or morecoils.

In accordance with a further embodiment, the cavity is produced by a hotfoil stamping technique.

In accordance with an embodiment of the invention, a “cavity” isunderstood to mean a recess from the substrate or an aperture throughtwo or more substrates, arranged one above the other, of a multi-layerprinted circuit board, that is to say what is known as a multi-layerPCB, wherein one of the substrates arranged one above the other formsthe base area.

In accordance with an embodiment of the invention, the coil core isfirst produced separately as a solid, and is then secured in the cavity,for example in a form-locked and/or force-locked manner, for example bybeing pressed into the cavity.

The coil cores can be produced for example by extrusion of apolymer/ferrite composite material. For example, endless profiles formedfrom the polymer/ferrite composite material are produced by theextrusion process, from which individual coil cores are obtained byseparating portions of the extrusion profile.

Such an extrudate can be produced as a flexible band and can be appliedby means of an adhesive to the substrate, more specifically inparticular where a higher overall thickness can be tolerated. In thiscase, the coil core may thus also extend beyond the surface of thesubstrate, wherein mixed forms are also possible, for example thefilling of the cavity in the substrate with a pasty or liquid materialand then, once this has cured, the application of one or more materiallayers thereof or of another core material to the already filled cavity.Such an additional film could also be adhered to one side of a printedcircuit board, in particular a multi-layer PCB, which is then inparticular advantageous if the sensor is to be arranged on the end face.

In accordance with an embodiment of the invention, the cross section ofa cavity or of the coil core may have different geometric shapes, whichmay be symmetrical or asymmetrical. The shape of the cavity andtherefore the shape of the coil core can be selected here such that themagnetic field obtains a geometry and strength optimized for therespective application.

Besides a rectangular shape, the coil core can be formed for example ina triangular, round or spherical manner. Such geometric shapes of thecavity can be produced for example by milling out material or by waterjet cutting, and the filling of the cavity with the core material can beachieved for example by printing, in particular by inkjet printing.

Furthermore, it is also possible for the core material within the coilcore to vary locally in order to achieve a desired shape of the magneticfield, wherein such a local variation of the material composition in thecoil core can be achieved for example by imprinting different corematerials in layers.

In accordance with an embodiment of the invention, the cavity extendsover a plurality of substrate layers in the vertical direction, whereinthe vias, that is to say the through-contactings, can be produced forexample by drilling, lasering, plasma-treating or water jet cutting.Combinations of such techniques are also possible, for example water jetcutting with laser guidance.

Embodiments of the invention allow the production of miniaturized coilswith the aid of cost-effective structuring and production techniquescapable of high-throughput, as are suitable for mass production.

In accordance with an embodiment of the invention, the substratecontains glass fibers, which are present in the substrate along one ormore preferred directions, for example in the form of a glass fibermatrix, or in an unordered manner; in particular, the substrate may be aglass-fiber-reinforced printed circuit board material.

In this case, glass fibers are severed due to the introduction of thecavity into the substrate, with the result that the cavity has anaccordingly rough surface finish. To smooth the surface of the cavity, amaterial is introduced into the cavity before the introduction of thefirst and second winding portions, said material extending over theflanks and the base area of the cavity. For example, the cavity iscompletely filled with the material. The material may be a plastic, aresin or another insulator.

This material is then removed again in part from the cavity, for exampleby machining or by application of a laser jet. A layer of the materialextending over the flanks and the base area remains in the cavity.

Since the material contains no glass fibers, it has an accordinglysmooth surface, that is to say the roughness of the surface of thismaterial layer is lower than the roughness of the flanks and the basearea of the cavity. For example, the layer thickness of this materiallayer may be less than 30 μm, in particular between 10 μm and 20 μm.

The first and second winding portions are then applied to this materiallayer. Surprisingly, the resultant coil then has an improved coilquality.

This is explained by the fact that, when applying the first and secondwinding portions directly to the flanks or the base area by means of the3D printing method, the imprinted winding portions have a reducedeffective line cross section, which is caused by the roughness of thesurface. This reduced effective line cross section leads to an increaseof the ohmic resistance and therefore to a reduction of the coilquality.

In accordance with embodiments of the invention, this problem isremedied in that the flanks and the base area of the cavity are smoothedby application of the material layer, and in that the first and secondwinding portions are not applied directly to the flanks and the basearea, but to the material layer extending over the flanks and the basearea.

Embodiments of the invention will be explained in greater detailhereinafter with reference to the drawings, in which:

FIG. 1 shows a schematic cross section of an electronic printed circuitboard according to the invention with an integrated coil,

FIG. 2 shows a perspective view of the printed circuit board accordingto FIG. 1,

FIG. 3 shows a schematic cross section of an embodiment of a printedcircuit board according to the invention with an applied coil,

FIG. 4 shows a perspective view of the printed circuit board accordingto FIG. 3,

FIG. 5 shows a cavity with applied and first and second windingportions,

FIG. 6 shows an enlarged partial illustration of FIG. 5, which shows aportion of the base area and of a flank of the cavity,

FIGS. 7-13 show an embodiment of a method for producing an electronicprinted circuit board with an integrated toroidal or annular coil,

FIG. 14 shows a plan view of an embodiment of a printed circuit boardaccording to the invention with an integrated annular coil, and

FIG. 15 shows a plan view of an embodiment of a printed circuit boardaccording to the invention with an integrated oval coil.

Corresponding or identical elements in the following exemplaryembodiments are denoted in each case by the same reference signs.

FIG. 1 shows a substrate 100, which may be a printed circuit boardmaterial, for example with glass-fiber reinforcement. For integration ofa coil 140 (see FIG. 2) into the substrate 100, a cavity 106 is firstproduced in the substrate 100, whereby a surface 102 of the substrate100 is opened.

For example, the cavity 106 is produced in the substrate 100 by amachining process by milling the cavity 106 into the substrate 100. Abase area 110 of the cavity 106, which for example runs parallel to thesurface 102, is thus produced. Furthermore, lateral flanks 112 and 114of the cavity 116, which each enclose an angle α with the surface 102,are further produced as a result. The angle α may be a right angle (asshown in FIG. 1) or an acute angle, in particular an angle of less than50°, for example 45°.

In the next step, the first winding portions 136 are applied to theflanks 112 and 114, and the second winding portions 138 are applied tothe base area 110 of the cavity 106.

This can be implemented in such a way that the first winding portions136 and the second winding portions 138 are applied in a single processstep by a 3D printing method, in particular by aerosol jet or inkjetprinting. This can occur in the form of a conductive polymer.

The cavity 106 is then filled with a core material so as to form thecoil core, for example is filled with a paste 116, which containsferromagnetic particles. Once the paste 116 has cured, third windingportions 139 are applied to the upper face 148 of the coil core formedby the cured paste, for example by means of a structuring technique or atwo-dimensional printing method.

The first winding portions 136 each have a lower first end 141 and anupper second end 147. Each two of the first ends 141 of two of the firstwinding portions 136 are electrically connected by one of the secondwinding portions 138, whereas two corresponding second ends 147 of twodifferent first winding portions 136 are electrically contacted by thethird winding portions 139, thus resulting in an approximately helicalcoil winding to form the coil 140.

The paste 116 can likewise be introduced into the cavity 106 by means ofprinting. A selection of the angle α of 45° is particularly advantageouswhen the paste 116 is introduced by means of screen printing, since theformation of air pockets in the paste 116 is then prevented in aparticularly efficient manner. The paste 116 may further be acted onduring the curing process with ultrasound or other vibrations in orderto prevent slug formation as the paste 116 cures. Alternatively, thecoil core can be formed by a solid instead of by the paste 116, saidsolid being introduced into the cavity 106.

FIG. 2 shows a perspective view of the resultant printed circuit board100 with the integrated coil 140.

FIG. 3 shows an alternative embodiment, in which the coil 140 is appliedto the substrate 100. To this end, the second winding portions 138 arefirst applied to the substrate 100. The core material, for example inthe form of the paste 116 or as a solid, is then applied to the secondwinding portions 138, wherein the core material covers the secondwinding portions 138, at least in part, for example as far as edgeregions of the second winding portions 138, as shown in FIG. 3.

Once the coil core has been formed, that is to say for example once thepaste 116 has cured, the first winding portions 136 are then applied tothe flanks 112 and 114 of the resultant coil core, and the third windingportions 139 are applied to the upper face 148. The resultant printedcircuit board 110 with the applied coil 100 is shown in FIG. 4 in aperspective view.

FIG. 5 shows an embodiment of the invention in which an oval annularcoil is to be integrated into the substrate 100. To this end, an ovalcavity 106 is milled into the substrate 100, wherein the substrate 100is glass-fiber-reinforced. FIG. 5 shows an intermediate product with theintegration of the coil 140 into the substrate 100, after which thefirst and second winding portions 136 and 138 respectively have beenimprinted by means of a 3D printing method.

FIG. 6 shows a partial view of FIG. 5 enlarged by five times, whereinthe rough surface of the cavity 106 and the resultant irregularstructure of the first and second winding portions 136 and 138respectively can be seen.

The rough surface of the cavity 106 is caused by glass fibers of thesubstrate 100, which are severed as the cavity 106 is milled. Theresultant irregular structuring of the winding portions 136 and 138leads to a reduction of the effective cross-sectional area thereof, andtherefore to an increase in the ohmic resistance, which ultimately leadsto a reduction of the coil quality of the coil 140 to be produced.

To remedy this problem, which may occur in the case of a substrate 100having a glass fiber content, the following approach in accordance withthe embodiment according to FIGS. 7 to 13 can be adopted:

The substrate 100 is first provided and is glass-fiber-reinforced, asillustrated in FIG. 7. The cavity 106 is then milled into the substrate100, wherein glass fibers are severed during the milling process, thusleading to a high surface roughness of the resultant cavity 106 (FIG.8).

The cavity 106 is then filled with a material 149. This material 149 maybe a resin for example. This is illustrated in FIG. 9.

The material 149 is then removed from the cavity 106 apart from a layer151, for example likewise by means of milling. The layer 151 of thematerial 149 remaining on the surface of the cavity 106 may have athickness from 10 μm to 20 μm, for example (see FIG. 10).

In the subsequent method steps illustrated in FIGS. 11, 12 and 13, theactual coil 140 is then produced by first applying the first and secondwinding portions to the flanks 112 and 114 of the cavity 106 coated bythe layer 151 and to the base area 110 coated by the layer 151 (FIG.11). The core material for forming the coil core is then introduced intothe cavity 106, for example by dispensing the paste 116 into the cavity106 in order to fill the cavity 106 with the paste 116 (FIG. 12).

The third winding portions 139 are then applied to the coil core thusformed.

FIG. 14 shows a plan view of the surface 102 of the substrate 100 withthe third winding portions 139 running in this plane, said third windingportions each electrically interconnecting two second ends 147 of thesecond winding portions 136, wherein the coil 140 is formed here as anannular coil.

The first and last winding portions 139 of the coil 140 are connectedhere via conductive tracks 142 and 144 to contact faces 143 and 145respectively.

The diameter of the coil 140 may be less than 5 mm, for example 3.5 mm.

FIG. 15 shows a corresponding coil 140 in an oval embodimentcorresponding to the embodiment according to FIGS. 5 to 13.

LIST OF REFERENCE SIGNS

100 substrate

102 surface

106 cavity

110 base area

112 flank

114 flank

116 paste

136 first winding portion

138 second winding portion

139 third winding portion

140 coil

141 first end

142 conductive track

143 contact face

144 conductive track

145 contact face

147 second end

148 upper side

149 material

151 layer

1. An electronic device comprising at least one coil integrated in asubstrate or applied to a substrate, the at least one coil includingfirst winding portions, which each have first ends and second ends, theat least one coil having second winding portions and third windingportions, wherein each two of the first ends are electricallyinterconnected by the second winding portions and two correspondingsecond ends of the first winding portions are electricallyinterconnected by the third winding portions to form the at least onecoil, the electronic device produced in accordance with a methodcomprising: printing, using a three-dimensional printing technique, atleast the first winding portions of the at least one coil; and whereinthe three-dimensional printing technique comprises at least one ofaerosol jet printing and inkjet printing.
 2. The electronic device ofclaim 1, wherein said device comprises at least one of a sensor and anactuator.
 3. The electronic device of claim 2, wherein the sensorcomprises at least one of a pressure sensor, force sensor, accelerationsensor, and a magnetic field sensor.
 4. An electronic device comprising:an electronic printed circuit board including at least one coilintegrated in or applied to the printed circuit board, the at least onecoil including: first winding portions, which each have first and secondends; second winding portions; and third winding portions; wherein eachtwo of the first ends of the first winding portions are electricallyinterconnected by the second winding portions and wherein twocorresponding second ends of the first winding portions are electricallyinterconnected by the third winding portions, with the result that coilwindings of the at least one coil are formed hereby; wherein at leastthe first winding portions are applied by means of a three-dimensional(3D) printing method; and wherein the 3D printing method includes atleast one of aerosol jet printing and inkjet printing.
 5. The electronicdevice of claim 4, wherein said device comprises at least one of asensor and an actuator.
 6. The electronic device of claim 5, wherein thesensor comprises at least one of a pressure sensor, force sensor,acceleration sensor, and a magnetic field sensor.